1. Field of the Invention
The present invention relates to an optical burst switching network and a method of reducing a burst loss rate due to blocking by means of duplicate optical burst transmission in the network.
2. Description of the Related Art
The optical burst switching (OBS) is an effective optical switching method capable of enhancing an optical channel usage rate by sharing optical wavelength resources between different ends from one another. In recent years, many protocols based on OBS have been proposed, and Just-Enough-Time (JET) OBS method may be employed as a representative example.
According to JET OBS, before collected packets, referred to as optical bursts are sent, a burst control packet (BCP) requesting a path reconfiguration of optical switches on the path is sent. Core nodes to be located in an intermediate of the path requires an electronic processing time for analysis on the BCP, so that a source node as an edge node positioned at an entrance of the optical network transmits the optical burst through an optical data channel with a time interval being equal to an offset time after transmission of the BCP. The transmitted optical burst is transparently delivered to a destination node as an edge node on the optical channel without having being subject to the electronic processing on the core node.
Hereinafter, an OBS network of the related art will be described with reference to FIG. 1.
FIG. 1 is a block view illustrating an OBS network according to the related art. A procedure of transmitting data bursts in the OBS network 100 will be described.
The node A 101 is an edge node and collects packets when Asynchronous Transfer Mode (ATM) packets or Internet Protocol (IP) packets are input to make a data burst. The data burst made by the node A 101 has a predetermined length. The edge nodes 101, 107, and 109 collect packets to make and transfer optical data burst packets or receive the optical data burst packet to separate them into each one.
The core nodes 103 and 105 act to optically switch the optical data burst. The node A 101, when the data burst is generated, generates a BCP and transmit it to a node B 103 as a core node, and transmits the data burst to the node B 103 after an offset time is elapsed. The BCP includes information about a destination address of the data burst, a generation address, a data burst size, a quality of service (QoS), an offset time and so forth.
The node B 103, by means of the received BCP, acknowledges the destination address of the data burst to be received later, determines an optical path, and schedules the time on the optical switching. The node B 103 can carry out optical switching onto the node D 107 or the node E 109 in response to the determination that the destination of the data burst transmitted from the node A 101 is the node D 107 or the node E 109.
In such an OBS manner, the optical burst having a long offset time has a relatively higher priority than an optical burst having a short offset time, so that a distinctive service can be provided making the offset times at the node A 101 as a source node different from one another to transmit the optical burst.
The OBS inevitably has an optical burst loss problem due to a contention for obtaining optical resources between control packets within a core node when the optical burst is transmitted on a data channel after an offset time is elapsed without any response messages after an optical BCP is transmitted on a signal channel using a unidirectional reservation manner.
In order to alleviate such optical burst loss problem, many methods have been proposed such as a method using a bidirectional signaling like Just-In-Time (JIT) OBS and wavelength routed OBS, a method using routing like depletion routing, a method using an optical burst scheduling within an OBS device like a latest available unused channel (LAUC), a method using optical burst segmentation, and so forth. These methods have a drawback that complicated signaling and processing is required.
In the meantime, a method has been proposed which sets an end-end session using a generalized multiprotocol label switching (GMPLS) signal protocol and applies JIT OBS to repeatedly transmit a copy of the optical burst on a backup path different from a transmission path of the original optical burst. According to this method, any one which is not subject to blocking between the original optical burst and the duplicate thereof received from two sessions having two different paths from each other is received at the destination node, thereby reducing a probability of optical burst loss. However, this method requires a traffic within the OBS network to increase two times, which causes a resultant blocking probability to increase so that a statistical multiplexing function of an optical layer as an advantage of the OBS cannot be utilized.